1. Field of the Invention
The present invention relates to the preparation of polyisobutylene (PIB). In particular the present invention relates to the preparation of a mid-range vinylidene content PIB composition. In this regard, the invention provides a novel liquid phase process for the polymerization of isobutylene to prepare a mid-range vinylidene content PIB composition using a modified BF3 catalyst. The invention also provides a novel composition of matter comprising a mid-range vinylidene content PIB composition.
2. The Prior Art Background
The polymerization of isobutylene using Friedel-Crafts type catalysts, including BF3, is a generally known procedure which is disclosed, for example, in “HIGH POLYMERS”, Vol. XXIV (J. Wiley & Sons, Inc., New York, 1971), pp. 713 ff. The degree of polymerization of the products obtained varies according to which of a number of known polymerization techniques is used. In this latter connection, it is to be understood that, in general, the molecular weight of the polymeric product is directly related to the degree of polymerization.
It is also known that PIB may be manufactured in at least two different major grades—i.e., regular and high vinylidene. Conventionally, these two product grades have been made by different processes, but both often and commonly use a diluted isobutylene feedstock in which the isobutylene concentration may range from 40-60% by weight. More recently it has been noted that at least the high vinylidene PIB may be produced using a concentrated feedstock having an isobutylene content of 90% by weight or more. Non-reactive hydrocarbons, such as isobutane, n-butane and/or other lower alkanes commonly present in petroleum fractions, may also be included in the feedstock as diluents. The feedstock often may also contain small quantities of other unsaturated hydrocarbons such as 1-butene and 2-butene.
Regular grade PIB may range in molecular weight from 500 to 1,000,000 or higher, and is generally prepared in a batch process at low temperature, sometimes as low as −50 to −70 EC. AlCl3, RAlCl2 or R2AlCl are used as catalysts. The catalyst is generally not totally removed from the final PIB product due to processing peculiarities. Molecular weight may be controlled by temperature since the molecular weight of the product varies inversely with temperature. That is to say, higher temperatures give lower molecular weights. Reaction times are often in the order of hours. The desired polymeric product has a single double bond per molecule, and the double bonds are mostly internal. Generally speaking, at least about 90% of the double bonds are internal and less than 10% of the double bonds are in a terminal position. Even though the formation of terminal double bonds is believed to be kinetically favored, the long reaction times and the fact that the catalyst is not totally removed, both favor the rearrangement of the molecule so that the more thermodynamically favored internal double bond isomers are formed. Regular PIB may be used as a viscosity modifier, particularly in lube oils, as a thickener, and as a tackifier for plastic films and adhesives. PIB can also be functionalized to produce intermediates for the manufacture of detergents and dispersants for fuels and lube oils.
High vinylidene PIB, a relatively new product in the marketplace, is characterized by a large percentage of terminal double bonds, typically greater than 70% and preferentially greater than 80%. This provides a much more reactive product, compared to regular PIB, and hence this product is also referred to as highly reactive PIB. The terms highly reactive (HR-PIB) and high vinylidene (HV-PIB) are synonymous. The basic processes for producing HV-PIB all include a reactor system, employing BF3 and/or modified BF3 catalysts, such that the reaction time can be closely controlled and the catalyst can be immediately neutralized once the desired product has been formed. Since formation of the terminal double is kinetically favored, short reactions times favor high vinylidene levels. The reaction is quenched, usually with an aqueous base solution, such as, for example, NH4OH, before significant isomerization to internal double bonds can take place. Molecular weights are relatively low. As used in this application, the terminology “relatively low” refers to a number average molecular weight (MN) which is less than about 10,000. HV-PIB having an MN of about 950-1050 is the most common product. Conversions, based on isobutylene, are kept at 75-85%, since attempting to drive the reaction to higher conversions reduces the vinylidene content through isomerization. Prior U.S. Pat. No. 4,152,499 dated May 1, 1979, U.S. Pat. No. 4,605,808 dated Aug. 12, 1986, U.S. Pat. No. 5,068,490 dated Nov. 26, 1991, U.S. Pat. No. 5,191,044 dated Mar. 2, 1993, U.S. Pat. No. 5,286,823 dated Jun. 22, 1992, U.S. Pat. No. 5,408,018 dated Apr. 18, 1995 and U.S. Pat. No. 5,962,604 dated Oct. 5, 1999 are directed to related subject matter.
U.S. Pat. No. 4,152,499 describes a process for the preparation of PIBs from isobutylene under a blanket of gaseous BF3 acting as a polymerization catalyst. The process results in the production of a PIB wherein 60 to 90% of the double bonds are in a terminal (vinylidene) position.
U.S. Pat. No. 4,605,808 discloses a process for preparing PIB wherein a catalyst consisting of a complex of BF3 and an alcohol is employed. It is suggested that the use of such a catalyst complex enables more effective control of the reaction parameters. Reaction contact times of at least 8 minutes are required to obtain a PIB product wherein at least about 70% of the double bonds are in a terminal position.
U.S. Pat. No. 5,191,044 discloses a PIB production process requiring careful pretreatment of a BF3/alcohol complex to insure that all free BF3 is absent from the reactor. The complex must contain a surplus of the alcohol complexing agent in order to obtain a product wherein at least about 70% of the double bonds are in a terminal position. The only reaction time exemplified is 10 minutes, and the reaction is carried out at temperatures below 0 EC.
In addition to close control of reaction time, the key to obtaining high vinylidene levels seems to be control of catalyst reactivity. This has been done in the past by complexing BF3 with various oxygenates including sec-butanol and MTBE. One theory is that these complexes are actually less reactive than BF3 itself, disproportionately slowing the isomerization reaction and thus allowing for greater differentiation between the vinylidene forming reaction (polymerization) and the isomerization reaction rates. Mechanisms have also been proposed that suggest the BF3 complexes are non-protonated and thus are not capable of isomerizing the terminal double bond. This further suggests that water (which can preferentially protonate BF3) must generally be excluded from these reaction systems. In fact, prior publications describing preparation of PIB using BF3 complexes teach low water feed (less than 20 ppm) is critical to formation of the high vinylidene product.
HV-PIB is increasingly replacing regular grade PIB for the manufacture of intermediates, not only because of higher reactivity, but also because of developing requirements for “chloride free” materials in the final product applications. Important PIB derivatives are PIB amines, PIB alkylates and PIB maleic anhydride adducts.
PIB amines can be produced using a variety of procedures involving different PIB intermediates which provide a reactive site for subsequent amination. These intermediates may include, for example, epoxides, halides, maleic anhydride adducts, and carbonyl derivatives.
Reference to HV-PIB as “highly reactive” is relative to regular grade PIB. HV-PIB is still not, in absolute terms, highly reactive toward formation of some of these intermediates. Other classes of compounds, polyethers for example, can be much more reactive in the formation of amines and amine intermediates. Amines derived from polyethers are known as polyether amines (PEA=s) and are competitive products to PIB amines.
The use of HV-PIB as an alklylating agent for phenolic compounds, is triggered by the higher reactivity and higher yields achievable with HV-PIB. These very long chain alkyl phenols are good hydrophobes for surfactants and similar products.
The largest volume PIB derivatives are the PIB-maleic anhydride reaction products. HV-PIB is reacted with maleic anhydride through the double bond giving a product with anhydride functionality. This functionality provides reactivity for the formation of amides and other carboxylate derivatives. These products are the basis for most of the lube oil detergents and dispersants manufactured today. As mentioned above, PIB-maleic anhydride products can also be used as intermediates in the manufacture of PIB amine fuel additives.
More recently, a novel more valuable process for the efficient and economical production of HV-PIB has been developed. This new process is described in U.S. Pat. No. 6,562,913 (hereinafter “the '913 patent”), which issued on May, 13, 2003 and is commonly owned with the present application. The entirety of the disclosure of the '913 patent is hereby incorporated into the present application by this specific reference thereto.
The '913 patent relates to a HV-PIB production process wherein the polymerization reaction takes place at higher temperatures and at lower reaction times than had previously been thought possible. In particular, the '913 patent describes a liquid phase polymerization process for preparing low molecular weight, highly reactive polyisobutylene. Generally speaking, the process of the '913 patent may involve cationic polymerization. However, under some conditions the polymerization reaction may be covalent. Particularly the latter may be true when ether is used as a complexing agent. In accordance with the disclosure of the '913 patent, the process includes the provision of a feedstock comprising isobutylene and a catalyst composition comprising a complex of BF3 and a complexing agent. The feedstock and the catalyst composition are introduced either separately or as a single mixed stream into a residual reaction mixture in a reaction zone. The residual reaction mixture, the feedstock and the catalyst composition are then intimately intermixed to present an intimately intermixed reaction admixture in the reaction zone. The reaction admixture is maintained in its intimately intermixed condition and kept at a temperature of at least about 0 EC. while the same is in said reaction zone, whereby the isobutylene in the reaction admixture is caused to undergo polymerization to form a polyisobutylene product. A product stream comprising a low molecular weight, highly reactive polyisobutylene is then withdrawn from the reaction zone. The introduction of the feedstock into said reaction zone and the withdrawal of the product stream from the reaction zone are controlled such that the residence time of the isobutylene undergoing polymerization in the reaction zone is no greater than about 4 minutes. In accordance with the '913 patent, it is possible to conduct the reaction so that the residence time is no greater than about 3 minutes, no greater than about 2 minutes, no greater than about 1 minute, and ideally, even less than 1 minute.
In accordance with the concepts and principles disclosed in the '913 patent, the process may be conducted in a manner such that the polyisobutylene thus produced has an MN in the range of from about 350 to about 5000, in the range of from about 600 to about 4000, in the range of from about 700 to about 3000, in the range of from about 800 to about 2000, and ideally in the range of from about 950 to about 1050. Moreover, it is possible to so control the process that a particular MN, such as for example, an MN of about 1000, may be achieved.
The '913 patent thus discloses a process which may be controlled sufficiently to insure the production of a polyisobutylene product having a vinylidene content of at least about 70%. More preferably the PIB product may have a vinylidene content of at least about 80%. In fact, vinylidene content of at least about 90% may be easily achieved through the use of the teachings of the '913 patent.
As set forth in the '913 patent, the complexing agent used to complex with the BF3 catalyst may desirably be an alcohol, and preferably may be a primary alcohol. More preferably the complexing agent may comprise a C1-C8 primary alcohol and ideally may be methanol.
To achieve the most desired results in accordance with the teachings of the '913 patent, the molar ratio of BF3 to complexing agent in the complex may range from approximately 0.5:1 to approximately 5:1. Preferably the molar ratio of BF3 to complexing agent in the complex may range from approximately 0.5:1 to approximately 2:1. Even more preferably the molar ratio of BF3 to complexing agent in the complex may range from approximately 0.5:1 to approximately 1:1, and ideally, the molar ratio of BF3 to complexing agent in the complex may be approximately 1:1.
In further accord with the teachings of the '913 patent, it is preferred that from about 0.1 to about 10 millimoles of BF3 may be introduced into the reaction admixture with the catalyst composition for each mole of isobutylene introduced into the admixture in the feedstock. Even more preferably, from about 0.5 to about 2 millimoles of BF3 may be introduced into the reaction admixture with said catalyst composition for each mole of isobutylene introduced into the admixture in the feedstock.
When the teachings of the '913 patent are applied, a process is provided whereby the polydispersity of the produced polyisobutylene may be no more than about 2.0, and desirably may be no more than about 1.65. Ideally, the polydispersity may be in the range of from about 1.3 to about 1.5.
In accordance with one preferred embodiment taught in the '913 patent, the reaction zone may comprise a loop reactor wherein the reaction admixture is continuously recirculated at a first volumetric flow rate, and the feedstock and the catalyst composition may be continuously introduced at a combined second volumetric flow rate. The ratio of the first volumetric flow rate to the second volumetric flow rate may desirably range from about 20:1 to about 50:1, may preferably range from about 25:1 to about 40:1 and ideally may range from about 28:1 to about 35:1. In order to achieve the preferred benefits of the loop reactor, the ratio of the first volumetric flow rate to the second volumetric flow rate may preferably be such that the concentrations of ingredients in the reaction admixture remain essentially constant and/or such that essentially isothermal conditions are established and maintained in the reaction admixture.
As described in the '913 patent, the feedstock and the catalyst composition may be premixed and introduced into the reaction zone together as a single stream at the second volumetric flow rate. Alternatively, the feedstock and the catalyst composition may be introduced into the reaction zone separately as two respective streams, the flow rates of which together add up to the second volumetric flow rate.
To achieve the ideal results described in the '913 patent, the reactor configuration, the properties of the reaction mixture, and the first volumetric flow rate may be such that turbulent flow is maintained in the reaction zone. In particular, the system may be such that a Reynolds number (Re) of at least about 2000 is achieved and maintained in the reaction zone. The system may also be such that a heat transfer coefficient (U) of at least about 50 Btu/min ft2 EF. is achieved and maintained in the reaction zone. To this end, the reactor may desirably be the tube side of a shell-and-tube heat exchanger.
In further accordance with the concepts and principles of the novel process described in the '913 patent, the feed stock may generally comprise at least about 30% by weight of isobutylene, with the remainder being non-reactive hydrocarbon diluents.
As mentioned above, high vinylidene PIB contains only a single double bond in each molecule, and most of these are in the terminal (alpha) position. Typically, more than 70%, and preferentially more than 80%, of the double bonds are in the terminal (alpha) position. Generally speaking, in known high vinylidene PIB products, the remaining 20 to 30% of the double bonds are in the beta position (between the second and third carbon atoms of the polymeric backbone). These beta position double bonds may be either 1,1,2-trisubstituted or 1,2,2-trisubstituted. Almost no tetra-substituted isomers are present in the high vinylidene PIB made in accordance with the teachings of the '913 patent, so that the total of the alpha and beta isomers is essentially about 100%.
On the other hand, while regular (conventional) PIB also has only one double bond per molecule, only about 5-10% of those double bonds are in the alpha position and only about 50% are in a beta position. The remainder of the PIB isomers include double bonds that are tetra-substituted and internal to the polymer as a result of isomerization reactions which occur during preparation. Because of the high level of the relatively non-reactive tetra-substituted olefin content, these products are sometimes referred to as low reactive PIB.
In the past, the only known PIB compositions have been (1) the highly reactive PIB containing essentially 100% alpha plus beta olefin isomers, with the vinylidene (alpha) isomer content being greater than 70%, and (2) the low reactive PIB in which the alpha plus beta isomer content is only about 60% and the vinylidene (alpha) content is less than about 10%.